Piezoeletric sensing element and torque sensor assembled with the same

ABSTRACT

A piezoelectric sensing element includes a ring type piezoelectric device, two ceramic structural adhesives, two electrode sheets, two structural adhesives, a ring type sheet, and a disk-shaped cylindrical ceramic sheet. The two ceramic structural adhesives, respectively located above and below the ring type piezoelectric device. The two electrode sheets, respectively located above and below the two ceramic structural adhesives. The two structural adhesives, respectively located above and below the two electrode sheets. The ring type sheet, located above or below one of the two structural adhesives. The disk-shaped cylindrical ceramic sheet, located below or above another of the two structural adhesives.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of co-pending application Ser. No.13/078,507, filed on Apr. 1, 2011, and for which priority is claimedunder 35 U.S.C. §120 and the entire contents of all of which are herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for processing a ring typepiezoelectric device, which is applied in a piezoelectric sensor,wherein the piezoelectric sensor is applied in a torque sensor; moreparticularly, the present invention relates to a ring type piezoelectricdevice which is formed in one piece.

2. Description of the Related Art

The piezoelectric effect is a process of converting electrical energyinto mechanical energy. This effect was first discovered in 1880 by theCurie brothers. In 1947, S. Roberts discovered the influence caused by adirect current electric field to BaTiO3 ceramic residual polarization,thereby triggering the applications and studies of ceramic materials inthe aspect of piezoelectric effects. Nowadays, piezoelectric elementshave been widely applied in various elements, such as sensors,actuators, transducers, and SAW filters. Because there are many types ofpiezoelectric elements, they can be classified as single layer or multilayer elements; according to their different structures, andrectangular, disk type or ring type (annular) elements, according totheir different shapes.

The most important element of ring type piezoelectric elements is a ringtype piezoelectric device. The manufacturing process of a conventionalring type piezoelectric device includes: respectively performingpolarization of the same direction P1 to a plurality of squarepiezoelectric embryos 11 a-14 a; arranging the square piezoelectricembryos as shown in FIG. 1A; respectively processing the squarepiezoelectric embryos into fan-shaped piezoelectric embryos 11 b-14 b;and putting the fan-shaped piezoelectric embryos together as a ringshape, shown in FIG. 1B.

The polarization direction of the abovementioned conventionalpiezoelectric device does not surround an annular direction; that is,the polarization direction is not perpendicular to an annular crosssectional surface. Therefore, the potential disadvantages comprise: poorpiezoelectric output, instability, and fragility of the structure.

Generally, a conventional torque sensor, composed of a plurality ofsmall and rounded quartz piezoelectric materials arranged in an annularshape, cannot be formed in one piece. Therefore, the conventional torquesensor has a complex manufacturing process that is relatively lengthy.

Therefore, there a need to provide a ring type piezoelectric device,method for processing the same, and torque sensor assembled with thesame to mitigate and/or obviate the aforementioned problems.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method forprocessing a ring type piezoelectric device, wherein the ring typepiezoelectric device is preferably formed in one piece.

It is another object of the present invention to provide a ring typepiezoelectric device applied in a piezoelectric sensor, wherein thepolarization direction of the ring type piezoelectric device isclockwise or counterclockwise perpendicular to the direction of anannular cross sectional surface.

It is yet another object of the present invention to provide a ring typepiezoelectric device applied in a piezoelectric sensor, which is appliedin a torque sensor.

To achieve the abovementioned objects, the present invention provides amethod for processing a ring type piezoelectric device, comprising:

Step 1: providing a ring type piezoelectric embryo. Preferably, the ringtype piezoelectric embryo is a lead zirconate titanate (PZT)piezoelectric embryo.

Step 2: printing at least a pair of electrode rings respectively on twosides of the ring type piezoelectric embryo so as to divide the ringtype piezoelectric device into a plurality of equal sections.Preferably, the step of printing at least a pair of electrode ringssubstantially prints three pairs of electrode rings. The electrode ringis preferably a silver electrode ring.

Step 3: immersing the divided ring type piezoelectric embryo into hightemperature silicon oil for performing high-voltage polarization to eachsection so as to make the polarization direction of the ring typepiezoelectric device clockwise or counterclockwise perpendicular to thedirection of an annular cross sectional surface.

Preferably, the present invention further performs a step of removingall electrode rings to form the ring type piezoelectric device. The ringtype piezoelectric device thus formed meets a d₁₅ efficientpiezoelectric coefficient.

Further, another object of the present invention is to provide apiezoelectric sensing element, which comprises a ring type piezoelectricdevice, two ceramic structural adhesives, two electrode sheets, twostructural adhesives, a ring type ceramic sheet, and a disk-shapedcylindrical ceramic sheet. Preferably, the ring type piezoelectricdevice meets a d₁₅ effective piezoelectric coefficient.

For the piezoelectric sensing element of the present invention, twosides of the ring type piezoelectric device are respectively printedwith a low-temperature electrode, wherein the polarization direction ofthe ring type piezoelectric device is clockwise or counterclockwiseperpendicular to the direction of an annular cross sectional surface.The two ceramic structural adhesives are respectively located above andbelow the ring type piezoelectric device. The two electrode sheets arerespectively located above and below the two ceramic structuraladhesives, wherein the two electrode sheets can be adhered to the ringtype piezoelectric device by pressurizing. The two structural adhesivesare respectively located above and below the two electrode sheets, suchthat the two electrode sheets can be respectively adhered to the ringtype ceramic sheet and the disk-shaped cylindrical ceramic sheet bymeans of the structural adhesives. Therefore, the ring type ceramicsheet is located above one of the two structural adhesives, while thedisk-shaped cylindrical ceramic sheet is located below another of thetwo structural adhesives.

In another embodiment, the ring type ceramic sheet and the disk-shapedcylindrical ceramic sheet can be replaced with a ring type materialsheet with a high friction coefficient and a disk-shaped cylindricalmaterial sheet with a high friction coefficient.

Further, yet another object of the present invention is to provide aring type piezoelectric device applied in a piezoelectric sensor, whichis applied in a torque sensor. The torque sensor comprises: apiezoelectric sensing element, a deformation structural element, and afixing element. The piezoelectric sensing element is the piezoelectricsensing element according to the abovementioned description. Thedeformation structural element is disposed within the deformationstructural element and used for receiving a force applied by a torquetest object.

The fixing element comprises a through hole. The through hole is capableof accommodating the torque test object, such that the torque testobject can contact the deformation structural element. The deformationstructural element can equivalently transfer the received force to thepiezoelectric sensing element, and generate an output signal accordingto the direct piezoelectric effect of the piezoelectric sensing element.

The fixing element, the deformation structural element, and thepiezoelectric sensing element are mounted together by means of a secondstructural adhesive or a screw bolt.

Other objects, advantages, and novel features of the invention willbecome more apparent from the following detailed description when takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome apparent from the following description of the accompanyingdrawings, which disclose several embodiments of the present invention.It is to be understood that the drawings are to be used for purposes ofillustration only, and not as a definition of the invention.

In the drawings, wherein similar reference numerals denote similarelements throughout the several views:

FIG. 1A and FIG. 1B illustrate processes of manufacturing a conventionalring type piezoelectric device,

FIG. 2A and FIG. 2B illustrate processes of manufacturing a ring typepiezoelectric device according to the present invention.

FIG. 3 illustrates an exploded view of a piezoelectric sensing elementaccording to the present invention.

FIG. 4 illustrates a perspective view of the piezoelectric sensingelement according to FIG. 3 of the present invention.

FIG. 5A illustrates an exploded view of a torque sensor according to oneembodiment of the present invention.

FIG. 5B illustrates a cross sectional view showing the torque sensor ofFIG. 5A being assembled.

FIG. 6 illustrates an exploded view of the torque sensor according toanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Please refer to both FIG. 2A and FIG. 2B, which illustrate processes ofmanufacturing a ring type piezoelectric device 2 according to thepresent invention. The processes comprise the following steps:

Firstly, step 1: providing a ring type piezoelectric embryo. Preferably,the ring type piezoelectric embryo is a lead zirconate titanate (PZT)piezoelectric embryo. Because the piezoelectric embryo is well known tothose who skilled in the art, there is no need for further description.

Next, step 2: printing at least a pair of electrode rings 20 a-20 frespectively on two sides of the ring type piezoelectric embryo, so asto divide the ring type piezoelectric device into a plurality of equalsections. Preferably, the electrode ring is a silver electrode ring. Thestep of printing at least a pair of electrode rings substantially printsthree pairs of electrode rings. Therefore, the ring type piezoelectricdevice is divided into six equal sections 21-26.

Then step 3: immersing the divided ring type piezoelectric embryo intohigh temperature silicon oil for performing high-voltage polarization toeach section, so as to make the polarization direction of the ring typepiezoelectric device clockwise or counterclockwise perpendicular to thedirection of an annular cross sectional surface.

For example, the electrode ring 20 a is set as “+” voltage, and theelectrode ring 20 b is set as “−” voltage. As a result, when the presentinvention performs high-voltage polarization to the ring typepiezoelectric embryo, the polarization direction of the section 21 ofthe ring type piezoelectric embryo can correspond to the arrowdirection, as shown in FIG. 2A. For example, the high-voltagepolarization applies a direct current polarization voltage of more thanone thousand V/mm, preferably 1.5 KV/mm as a minimum, to an equivalentmid-diameter between the electrodes of the piezoelectric embryo. Thenthe electrode ring 20 b is changed to “+” voltage, and the electrodering 20 c is set as “−” voltage for the high-voltage polarization, suchthat the polarization direction of the section 22 of the ring typepiezoelectric embryo can correspond to the arrow direction shown in FIG.2A. The present invention sequentially performs the high-voltagepolarization to complete the high-voltage polarization to all sections21-26 of the piezoelectric embryo, thereby obtaining the polarizationdirection shown in FIG. 2A.

Further, in order to reduce the time required for polarization, thepresent invention can set the electrode rings 20 a and 20 d as “+”voltage, and the electrode rings 20 b and 20 e as “−” voltage for thehigh-voltage polarization, such that the polarization direction of thesections 21 and 24 of the ring type piezoelectric embryo can correspondto the arrow directions shown in FIG. 2A. Therefore, only three times ofpolarization are required to complete the polarization to the entirering type piezoelectric embryo.

Although three pairs of electrode rings are depicted in the figures,please note that the number of electrode rings is not limited to theabove description. For example, four pairs of electrode rings can alsoachieve the objects of the present invention, which means that thepolarization direction of the ring type piezoelectric device isclockwise or counterclockwise perpendicular to the direction of anannular cross sectional surface.

Preferably, after the polarization, the present invention furtherperforms a step of removing all electrode rings 20 a-20 f, so as to forma required ring type piezoelectric device 2. As shown in FIG. 2B, thering type piezoelectric device 2 is formed in one piece, and itspolarization direction P2 is clockwise or counterclockwise perpendicularto the direction of the annular cross sectional surface. Preferably, thering type piezoelectric device formed according to the method of thepresent invention meets a d₁₅ effective piezoelectric coefficient.

Further, another object of the present invention is to provide apiezoelectric sensing element. Please refer to FIG. 3 and FIG. 4. FIG. 4illustrates a perspective view of an assembled piezoelectric sensingelement 4 according to FIG. 3. The piezoelectric sensing element 4 ofthe present invention comprises a ring type piezoelectric device 2, twoceramic structural adhesives 31, two electrode sheets 33, two structuraladhesives 34, a ring type ceramic sheet 35, and a disk-shapedcylindrical ceramic sheet 36. Preferably, the ring type piezoelectricdevice 2 meets a d₁₅ effective piezoelectric coefficient.

For the piezoelectric sensing element 4 of the present invention, twosides of the ring type piezoelectric device 2 are respectively printedwith a low-temperature electrode (not shown in figures). For example,two sides of the ring type piezoelectric device 2 can be coated withlow-temperature silver pastes as the low-temperature electrodes. Thepolarization direction of the ring type piezoelectric device 2 isclockwise or counterclockwise perpendicular to the annular crosssectional direction. Precisely, the ring type piezoelectric device 2 canbe formed by means of utilizing the above mentioned method.

As shown in FIG. 3, the two ceramic structural adhesives 31 and 31 arerespectively located above and below the ring type piezoelectric device2. The two electrode sheets 33 and 33 are respectively located above andbelow the two ceramic structural adhesives 31 and 31, wherein the twoelectrode sheets 33 and 33 can be adhered to the ring type piezoelectricdevice 2 by pressurizing the two ceramic structural adhesives 31 and 31.The two structural adhesives 34 and 34 are respectively located aboveand below the two electrode sheets 33 and 33, such that the twoelectrode sheets 33 and 33 can be respectively adhered to the ring typeceramic sheet 35 and the disk-shaped cylindrical ceramic sheet 36 bymeans of the structural adhesives 34 and 34. Therefore, the ring typeceramic sheet 35 is located above one of the two structural adhesives34, while the disk-shaped cylindrical ceramic sheet 36 is located belowanother of the two structural adhesives 34.

In another embodiment of the present invention, the ring type ceramicsheet 35 and the disk-shaped cylindrical ceramic sheet 36 can also bereplaced with a ring type material sheet with a high frictioncoefficient and a disk-shaped cylindrical material sheet with a highfriction coefficient.

Either the ceramic sheet or the material sheet with a high frictioncoefficient is a multi-layer piezoelectric element, which is well knownto those who skilled in the art; therefore, there is no need to describethe theory and function of the multi-layer structure in more detail. Thepiezoelectric sensing element 4 of the present invention utilizes thering type piezoelectric device 2 formed in one piece, so as to simplifythe manufacturing process and reduce the manufacturing time. Moreover,because the polarization direction of the ring type piezoelectric device2 is clockwise or counterclockwise perpendicular to the annular crosssectional surface, the present invention further comprises theadvantages of: improved piezoelectric output efficiency, high stability,and better structural strength.

Further, yet another object of the present invention is to provide atorque sensor. As shown in FIG. 5A and FIG. 5B, the torque sensor 5comprises: a piezoelectric sensing element 4, a deformation structuralelement 51, and a fixing element 52. The piezoelectric sensing element 4is the piezoelectric sensing element 4, as shown in the above FIG. 4.The piezoelectric sensing element 4 is disposed within the deformationstructural element 51 and is used for receiving a force applied by atorque test object 90.

The fixing element 52 comprises a through hole 522. The fixing element52 is corresponding to the deformation structural element 51 so as tosandwich the piezoelectric sensing element 4 between the fixing element52 and the deformation structural element 51. The through hole 522 iscapable of accommodating the torque test object 90, such that the torquetest object 90 can contact the deformation structural element 51.

If the piezoelectric sensing element 4 adopts the aforementioned ringtype ceramic sheet 35 and the aforementioned disk-shaped cylindricalceramic sheet 36, the torque sensor 5 can utilize a second structuraladhesive (not shown in figures) to respectively adhere two sides (i.e.outers of the ring type ceramic sheet 35 and the disk-shaped cylindricalceramic sheet 36) of the piezoelectric sensing element 4 to the fixingelement 52 and the deformation structural element 51.

In another embodiment, a screw bolt 60 (such as a coaxial screw bolt)can be utilized to mount the piezoelectric sensing element 4 and thedeformation structural element 51 to the fixing element 52.

Please refer to FIG. 5B, which illustrates a cross-section view showingpartial assembly of the torque sensor according to the present inventionto explain the test of the torque sensor. When the torque test object 90contacts the deformation structural element 51 and starts to twist alongthe arrow direction, the torque of the torque test object 90 is appliedto the deformation structural element 51 to generate deformation γaccording to a basic equation: τ=G*γ. Because the piezoelectric sensingelement 4 is mounted to the deformation structural element 51, thedeformation γ will be equivalently transferred to the piezoelectricsensing element 4, thereby generating an output signal according to thedirect piezoelectric effect.

Take a “pneumatic wrench” as an example. Because it has a greaterimpact, it is necessary to reduce the torque. An appropriate shearmodulus (modulus of rigidity, G) of the material of the deformationstructural element 51 can be selected according to the strength of theapplied torque under test. The (inner/outer) diameter and thickness ofthe piezoelectric sensing element 4 can be designed according torelevant sizes of the torque test object. However, the effectiveness ofthe manufacturing process, such as polarization, must be maintainedduring the manufacture of the piezoelectric sensing element. During theprocess of designing the torque sensor, the maximal circumference IDdeformation of the piezoelectric sensing element 4 or 4° should begreater than the deformation γ. Therefore, the range of measuring thetorque and the connection interface of the torque test object can bedetermined according to the material natures and sizes of differentdeformation structural elements. As a result, different designs can beimplemented according to different measuring methods, conditions andrequirements. Therefore, the abovementioned “pneumatic wrench” may notlimit the scope of the present invention.

FIG. 6 shows another embodiment of the present invention. The torquesensor 6 further comprises a wireless communication device 57 and a base55 for fixing the wireless communication device 57. In this embodiment,the measurement can be sent by the wireless communication device 57.

Although the present invention has been explained in relation to itspreferred embodiments, it is to be understood that many other possiblemodifications and variations can be made without departing from thespirit and scope of the invention as hereinafter claimed.

What is claimed is:
 1. A piezoelectric sensing element, comprising: aring type piezoelectric device, with two sides respectively printed witha low-temperature electrode, wherein the polarization direction of thering type piezoelectric device is clockwise or counterclockwiseperpendicular to the direction of an annular cross sectional surface;two ceramic structural adhesives, respectively located above and belowthe ring type piezoelectric device; two electrode sheets, respectivelylocated above and below the two ceramic structural adhesives, whereinthe two electrode sheets can be adhered to the ring type piezoelectricdevice by pressurizing the two ceramic structural adhesives; twostructural adhesives, respectively located above and below the twoelectrode sheets; a ring type sheet, located above or below one of thetwo structural adhesives; and a disk-shaped cylindrical ceramic sheet,located below or above another of the two structural adhesives.
 2. Thepiezoelectric sensing element as claimed in claim 1, wherein the ringtype sheet is a ring type ceramic sheet.
 3. The piezoelectric sensingelement as claimed in claim 2, wherein the disk-shaped sheet is adisk-shaped cylindrical ceramic sheet.
 4. The piezoelectric sensingelement as claimed in claim 1, wherein the ring type sheet is a ringtype material sheet with a high friction coefficient.
 5. Thepiezoelectric sensing element as claimed in claim 4, wherein thedisk-shaped sheet is a disk-shaped cylindrical material sheet with ahigh friction coefficient.
 6. The piezoelectric sensing element asclaimed in claim 1, wherein the ring type piezoelectric device meets ad₁₅ effective piezoelectric coefficient, and the ring type piezoelectricdevice is formed in one piece.
 7. A torque sensor comprising: apiezoelectric sensing element as claimed in claim 6; a deformationstructural element for receiving a force applied by a torque testobject, wherein the piezoelectric sensing element is disposed within thedeformation structural element; and a fixing element comprising athrough hole, wherein the fixing element is corresponding to thedeformation structural element so as to sandwich the piezoelectricsensing element therebetween, and the through hole is capable ofaccommodating the torque test object, such that the torque test objectcontact the deformation structural element through the piezoelectricsensing element.
 8. The torque sensor as claimed in claim 7, wherein thering type sheet is a ring type ceramic sheet.
 9. The torque sensor asclaimed in claim 8, wherein the disk-shaped sheet is a disk-shapedcylindrical ceramic sheet.
 10. The torque sensor as claimed in claim 7,wherein the ring type sheet is a ring type material sheet with a highfriction coefficient.
 11. The torque sensor as claimed in claim 10,wherein the disk-shaped sheet is a disk-shaped cylindrical materialsheet with a high friction coefficient.
 12. The torque sensor as claimedin claim 7, wherein the ring type piezoelectric device meets a d₁₅effective piezoelectric coefficient, and the ring type piezoelectricdevice is formed in one piece.
 13. The torque sensor as claimed in claim7 further comprising a wireless communication device and a base forfixing the wireless communication device.
 14. The torque sensor asclaimed in claim 7, wherein the fixing element, the deformationstructural element, and the piezoelectric sensing element are mountedtogether by means of a second structural adhesive or a screw bolt.